HIGH ACCURACY MULTI-GAS MONITORING USING AUTOMATED SELF- CALIBRATION

HIGH ACCURACY MULTI-GAS MONITORING USING AUTOMATED SELF- CALIBRATION

SCENTROID is the global leader in sensory technology providing intelligent environmental solutions across a wide range of industries Scentroid manufactures all its products in Canada and exports to 42 countries worldwide. ABOUT SCENTROID

SOME OF OUR CLIENTS

PRODUCTS

Scentroid has 3 main types of chemical analyzer Pollutracker Portable with up to 10 sensors DR1000 Flying Lab can be attached to any drone and can be used to sample and analyze ambient air instantly Scentinal SL50 Compact Air Quality and odour Monitoring Station provides extreme accuracy using innovations in self calibration and data analysis. CHEMICAL ANALYZER

CHALLENGE

A client is using data from a Scentinal as evidence in a litigation case. The question is: How do we know zero ppm means really zero? How do we know 10 ppb is really 10 ppb? DATA RELIABILITY

Common Sensing Technologies Photo ionization Detector (PID) Detect VOCs in ppb by use of high energy UV photons. Nondispersive Infrared Sensor (NDIR) Detect various compounds such as CO2. Electro Chemical EC detect a wide range of compounds by oxidizing the target gas at the electrode. SENSING TECHNOLOGIES

Common Sensing Technologies Photo ionization Detector (PID) lamp will fail after X hours showing always zero ppm. Lamp can be coated with dust reducing sensitivity. Nondispersive Infrared Sensor (NDIR) similar to PID. Electro Chemical EC Slow drift of zero based on time and exposure. Change of sensitivity due to time, exposure, and other environmental parameters. FAILURE MODES

AUTOMATED CALIBRATION

Zero Calibration provide zero air to check and adjust the zero voltages. Full Span calibration determine the nonlinear curve of signal to gas concentration. Verification check response of sensor to Minimum Detection Limit. Concentration OBJECTIVE

Permeation Tube vs Calibration Gas Transport Calibration gas is difficult to ship as a hazardous material. Difficult to Source Gases are difficult to source in many countries. Settling Gas cylinders must be shaken to ensure uniformity otherwise heavier gases may settle at the bottom of the cylinder and create a non uniform concentration. CREATING REFERENCE GAS

System Overview CALIBRATION SYSTEM Zero Air Generator A miniaturized zero air generator provides clean air for zero reference. Flow is digitally monitored to ensure accuracy. Permeation Oven/Refrigerant temperature controlled permeation oven can achieve any temperature between 10 to +45C. Oven can take up to 8 permeation tubes (default 4) for complex gas mixtures. Control System The oven is controlled by a dedicated microcontroller. Adjusting temperature and flow can create mixtures of any concentration. At 3C the permeation tube is in stasis to prolong service life. Zero Air Generator F1 12 Cabinet Air Pump 1 Primary Scrubber Secondary Scrubber Digital Flow meter Permeation Oven/Refrigerator Calibration Gas 3 way valve Sensors

180 Zero Drift Drift compensation The following graph shows the zero voltage in equivalent ppb of H2S over 10 months. With zeroing every 12 hours the drift is fully compensated for. Drift over 12 hours is less than detection limit. Zero Drift (ppb) 160 140 120 100 80 60 40 20 0-20 1 2 3 4 5 6 7 8 9 10 Months Without Compensation Auto Calibrated RESULTS FOR ZERO CALIBRATION

Sensitivity Vs Time (H2S) Sensitivity Change The following graph shows the sensitivity calculated manually every month for 10 months as well as sensitivity calculated by instrument every 72 hours. Typical loss is 20 25% per year in laboratory conditions This instrument was exposed to H2S levels of 200 800 ppb continuously. mv/ppm 1400 1300 1200 1100 1000 900 800 700 600 500 0 50 100 150 200 250 300 days RESULTS FOR SENSITIVITY

Automated Calibration can provide: Fault Detection: Sensor fault are detected almost instantly. Higher accuracy: adjusting for sensor drift and loss of sensitivity accuracy can reach those achieved in the laboratory. Higher reliability: documented response of sensors will provide proof the sensors are always working within specifications. The Automated calibration can allow the low cost sensing solutions to perform similar to much more expensive analyzers. CONCLUSION

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